A variety of industrial processes generate aqueous streams containing contaminating amounts of organic compounds. Before such streams can be discharged into a receiving body of water, the organics content must be substantially reduced to meet environmental regulatory standards.
For example, offshore oil platform operations may generate produced water streams. Some produced water contains naturally-occurring brines associated with and in contact with naturally-occurring petroleum in subsurface reservoirs and is produced as a consequence of producing the petroleum. The water may contain significant amounts of dissolved organic acids and other contaminating hydrocarbons. A particular problem with this type of produced water is that often carboxylic acid salts such as salts of naphthenic acids may be present. If not removed, these contaminants are measured as oil and grease when the water is tested pursuant to EPA gravimetric test methods. Thus, it is desirable to treat such water so that it may be discharged without exceeding Environmental Regulatory Standards for effluent water, which often require effluent concentration of organic pollutants which are below the solubility limit for the organic compounds in water.
Other examples of oily waters may include any number of streams emanating from a commercial facility, such as, for example, an oil refinery or chemical production plant, or a facility which utilizes petroleum fuel oils say, for instance, electric power plants for which fuel oil must be desalted in a counter current water washing process. Water produced with crude oil or natural gas in oil and gas producing operations are also examples of oily waters.
The above described produced and oily waters are not adequately treated by mechanical means, settling (i.e. gravity separation) or conventional floatation techniques. We have found conventional oil/water separation techniques to be inadequate in removing these water-soluble organics.
The aqueous compositions resulting from these treatment processes often contain very small suspended hydrocarbon particles, and often dissolved hydrocarbons in the continuous water phase.
Previous attempts have been made to remove dissolved organic contaminants by acidification. For example, U.S. Pat. No. 4,401,570 issued August 1983 to Blytas et al., discloses a method of removing organic esters from waste water using acidification. However merely acidifying the water has been found inadequate, to effect a separation of these dissolved organics.
In U.S. Pat. No. 4,839,054, issued Jun. 13, 1989 to Ruebush et al., a better separation of dissolved organics from a produced water is described through acidifying the produced water with a strong acid, contacting the acidified water with a free oil to form a mixture, agitating and separating the phase to produce a free oil phase and a clean water phase. The requirements of materials of construction resistent to strong acids, and lack of a fully effective means of coalescing droplets of previously dissolved organics coming out of solution, make the process described in U.S. Pat. No. 4,839,054 less than fully commercially attractive.
Recently, improved mechanical means, specifically, improved rotary vortex or hydrocyclone separators have been used to separate heterogeneous liquids such as water with a small oil content on offshore oil platforms. A cyclonic separator or hydrocyclone is a piece of equipment which utilizes fluid pressure energy to create rotational fluid motion. This rotational motion causes relative movement of less-dense particles suspended in the fluid thus permitting separation of particles, one from another or from the fluid. In some cases, the less dense particles are fluid droplets dispersed in another, different density fluid. In liquid-liquid hydrocyclones, the rotational fluid motion is produced by tangential injection of fluid under pressure into a vessel. The vessel at the point of entry for the fluid is usually cylindrical and can remain cylindrical over its entire length though it is more usual for it to become conical. Hydrocyclones have also been used extensively as gravity separators in coal preparation plants and the minerals processing industries. Two general categories of hydrocyclones are used for gravity separation.
One such floatation apparatus for obtaining separation of fine particles in a centrifugal field is described in U.S. Pat. No. 4,399,027 issued Aug. 16, 1983 to Miller.
Another hydrocyclone separator described as useful in separating small quantities of oil from large streams of discharged water is described in U.S. Pat. No. 4,964,994 issued Oct. 23, 1990 to Wakley et al.
A significantly improved centrifugal field separator; a rotating sleeve hydrocyclone is described in U.S. patent application Ser. No. 07/530,877 filed May 30, 1990, now U.S. Pat. No. 5,062,955, assigned to the assignee of the present invention. The hydrocyclone disclosed in U.S. application Ser. No. 07/530887 is particularly useful in handling the separation of fluids in the presence of gas. The disclosure of U.S. patent application Ser. No. 07/530,877 is fully incorporated by reference herein.
Neither the aforementioned strong acid acidification and oil sponge process, nor the improved hydrocyclonic separators alone are fully effective in removing dissolved and/or very finely dispersed organic droplets, in a commercially feasible process.
Therefore, an improved process for removal of dissolved organics from industrial waters is much desired.